text:
Can a holder of a Commercial Pilot License be compensated for business flight expenses?
I’m buying a plane with business partners as we travel often for business.  If I obtain my commercial license can I then be reimbursed or technically “compensated” for all flight expenses whether one, two or no partners are on the airplane with me.  I have zero interest in taking compensation for non-business related flights.

To answer your question.  Yes, you can be compensated for all those scenarios provided your company owns the aircraft.  You will fall in the second bullet point below.  You can use your commercial certificate to fly under Part 91 and get compensated for it.

If you have a commercial pilot certificate you are allowed to get paid to fly an airplane.  The rules for commercial pilots differ on who is offering the aircraft.

Either you or your company is offering an aircraft to transport passengers who pay your company for that transportation.  This will require a Part 119 operating privilege issued under either Part 121 (airline) or Part 135 (contract) operations.

You are flying an aircraft that is provided by the passengers or their company.  In this case, you can operate under Part 91 rules and do not need an operating privilege under Part 119.

The second example is done all the time with corporate flight departments.  The company owns the aircraft to fly their employees to meetings and such.  They hire commercial / ATP pilots to fly those aircraft for them.
They even take passengers / family members who are not a part of the company to their desired location.  The difference here is those passengers do not pay the company for the flight.
If I purchase a Cessna 172 and want to hire a pilot to fly me to my destination that would be legal under Part 91 as I own the aircraft and I hire the pilot.  If the pilot owns the aircraft and I hire them and their plane, they will need a Part 119 operating privilege.
Some may say there are exceptions where the pilot owner shares the pro-rata cost of the flight with me.  That only works if the owner pilot has a bona-fide purpose of going to that destination airport that originally didn't include your wishes.  That would be a private pilot privilege and not a commercial pilot privilege though.
Even though you will have a commercial pilot certificate you are not always acting as a commercial pilot when you fly.  Sometimes you will be acting like a private pilot.  Think of a truck driver who parks their 18-wheeler semi-truck for the day and then hops in their SUV and goes home.  One is a commercial operation, and the other is a private operation.

Great and clear answer! I like that you make a distinction of "acting like." I've heard the term of art "exercising the privileges of..." For example, you could exercise your private pilot privileges and expense the flight under 61.113, or your could be hired by your company to fly the company plane and exercise your privileges afforded by your commercial pilot certificate.

14 CFR 61.113(b) allows pilots to receive compensation when acting as PIC “in connection with any business or employment.”
Note, this only works if you're the sole occupant of the airplane. If you have passengers, even if you're all flying to the same business meeting, the most you can do is split the expenses between all passengers. The Mangiamele ruling has this to say:

Thus, because you are transporting people to the meeting, you may not
seek reimbursement from your employer for this flight under 14 C.F.R.
§ 61.113(b ).

There might be another scenario that works for you since you mentioned getting your commercial pilot license: Have the company purchase the airplane and hire you as the pilot to fly it. (See @wbeard52's answer)
Here is another good resource from the AOPA if you want to read more about expensing a business flight.

61.133 covers Commercial licenses.

Your answer is a good one, and technically correct, but the "passengers" in this case are both owners of the aircraft, and owners of the business.  I don't think your suggestion that the company purchase the aircraft and hire him as a pilot is really necessary, or correct.

@MichaelHall I think it depends on how the ownership is actually structured and where the reimbursements are coming from. You can be both the owner of the business and an owner of the aircraft, but if the business itself doesn't own the aircraft, but paying the owner/operator for the expenses associated with the use of the airplane, the owners of the aircraft (even though they own the company receiving the services) would need a Part 135 license.

I'm not an aviation or corporate lawyer, but pretty sure you only need a part 135 license to haul paying customers.  If you are business partners and co-owners of an airplane you use in the furtherance of your business, why would you burden one partner's personal salary with aircraft operating expenses and not write it off as a joint business expense?  I don't see anything in the regs requiring you to do so.

Yes, you don't even need to wait until you get a commercial certificate either.  CFR part 61.113 states:

(b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:

(1) The flight is only incidental to that business or employment; and

(2) The aircraft does not carry passengers or property for compensation or hire.

You don't give up private pilot privileges when you earn a commercial certificate, so if a private pilot may be compensated under the stated conditions it makes sense that a commercial pilot could as well, for confirmation we look to CFR 14, part 61.133 which states:

(1) General. A person who holds a commercial pilot certificate may act
as pilot in command of an aircraft -

(i) Carrying persons or property for compensation or hire, provided the person is qualified in accordance with this part and with the applicable parts of this chapter that apply to the operation; and

(ii) For compensation or hire, provided the person is qualified in accordance with this part and with the applicable parts of this chapter that apply to the operation.

So yes, you may reimburse yourself for flying expenses related to your and your partner's business.

Why the downvote? Please have the courtesy and fortitude to provide constructive feedback whoever you are...

I didn't downvote but you are quoting private pilot regs when the OP is asking about commercial operations.

@wbeard52, did you read and process the entire message of my answer?  He asked "IF" he obtains a commercial cert.  I pointed out first that you don't even need to have a commercial certificate to do what he is asking, and finished by quoting the commercial regs for good measure.

I took his question as he will have his commercial certificate and wants to know if he can be compensated after getting his commercial certificate.  I didn't read your answer all the way.  I saw the reference to private regs and moved on.  I think though the commercial regs you quoted are incomplete to fully answer why he can be compensated from his company.

@wbeard52, well, he did say "if"...


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What does a numbered dot mean on a sectional chart?

What does this point (125) mean on a Sectional Chart?
Is it the field elevation, or just the highest elevation on the area?

It’s a local elevation at a particular point, generally in a flat area as a reference base elevation for the area.

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What does 'category' mean in the NEW NAVAID menu of the Airbus FMS?
I tried to create a NEW NAVAID in the Flight Management System because I was simulating a flight to an airport that is not in the database of the FMS.
What Category is Airbus referring to in the MCDU menu:

DATA > Next Page > NAVAID > 2R, (see image below).

I don't understand why a LOC DME has categor y= 0? What it's RNP or ILS DME? which category should I insert?

Reference: FCOM> Aircraft System> Auto Flight-Flight Management> Control and Indicators> MCDU-Page Description> NAVAID/PILOT'S NAVAID> NEW NAVAID Pages.

It's the precision instrument approach category, CAT I (1), CAT II (2) or CAT III (3). LOC DME doesn't have an approach category because it provides only lateral guidance with no vertical support, so a precision instrument approach is not possible.

Noted, thank you :)

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Is the AOA on the horizontal stabilizer positive?
I am making a flight sim and would like some help.
If I am correct, the angle of attack on the horizontal stabilizer should look something like this:
aoa(Hstab) = aoa(Wing) - downwash + Hstab incidence
From research, the AOA of the Hstab should be negative most of the time, however, that just doesn't seem to happen. For example, if the plane is flying at an AOA of 8 degrees, the downwash won't be more than 3 or 4 degrees, and the horizontal stabilizer incidence won't be less than -1 or -2 degrees. So how is the aoa of the Hstab ever negative, if 8 - 4 - 2 is positive?

For stability the stab's AoA need not be negative, it just needs to be less than the wing's.

Is the stab's own incidence really no lower than -2 degrees?

@CamilleGoudeseune , so let's say for instance this scenario. The AOA of the wing is 8 degrees. The downwash angle is subsequently 3 degrees, and the horizontal stabilizer incidence is -1 degree.
8 - 3 - 1 is 4 degrees. This means that the AOA of the horizontal stabilizer is 4 degrees, therefore it will produce lift upwards in the same direction of the wing, therefore it will contribute to the pitching forwards moment of the wing, pitching the plane forwards. How is that stable?

Why are you considering the AoA of the wing? The AoA of the horizontal stabilisers is... well, the AoA of the horizontal stabilisers. It's easier if you use the fuselage as reference and not the AoA of the wing so that the AoA of the hstab is AoA of the fuselage + its incidence - downwash. As a rule of thumb the downwash is half of the AoA of the wing.

@sophit If you use the AoA relative to the zero-lift angle it is indeed more relevant than any angle of the fuselage. And your downwash rule-of-thumb needs a rather low aspect ratio to be in the ballpark.

@PeterKämpf: sure, one can definitely use the AoA relative to the wing's zero-lift, the important thing is to be consistent which it doesn't seem to be the case here since the incidence of the horizontal stabilisers seems to be given in respect to the fuselage in the question.

I see confusion from the lack of a distinction between stability and trim in a lot of the discussion. I can set the stab AOA to be in line with the wing's zero lift AOA and my airplane will be a very stable ballistic dart. To make it fly I have to force the wing to a positive AOA, by trimming it with the rear surface to oppose the wing's pitching moment until an equilibrium is reached at some wing AOA. Stability forces do their thing by acting with restorative forces on either side of that equilibrium point as required. Thus stability and trim are separate but interrelated things are they not?

@zander: btw when you write that "the AOA of the Hstab should be negative" do you mean that the stabilisers is generating a negative lift?

@sophit yes that's what I mean. Otherwise both the wing and horizontal stabilizer will be producing "positive" lift and the plane will just pitch forwards.

@zander: perfect. If you choose the AoA of the wing to do your calculations then just remember that the incidence of the horizontal stabilisers have to be given in respect to the one of the wing. And no, positive lift from the horizontal stabilisers doesn't imply an unstable airplane (think about a canard as an extreme example).

Your formula is correct, and there is no need for the AoA of the horizontal tail to be negative. It only needs to be less than that of the wing (relative to the zero-lift angle). Stability is determined not by the direction of the lift force on the tail, but its gradient over AoA.

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Are Air Traffic Flow Management Algorithms mostly based on linear programming techniques?
I'm really interested in knowing the methods used by the Air-Traffic-Flow-Management (ATFM) providers to increase the throughput of the airspace by balancing safety, efficiency and cost. I've been reading different research papers and most of them conclude on using algorithms based on linear programming to manage the arrival and departure slots.
For instance, there are many articles explaining a possible resolution of the Ground Holding Problem, that allocates departure slots so that no sector is violated, by using linear programming and mathematical optimization techniques. Airport capacity as well can be improved by the use of linear programming.
I know that linear programming is based on minimizing/maximizing a certain objective function, subject to a set of constraints.
I see that these techniques can be a good idea to have a big picture of an optimal configuration of slots, for instance. But are these linear programming algorithms actually used?
Is linear programming so much effective to carry out air traffic management according to this method? What other methods are powerful and used nowadays to manage air traffic?

I don't know what NMOC actually uses, but I think it is not linear programming. The algorithm must be an online one, that is it must assign time slots to flights as the flight plans are filed, without much room for moving the already scheduled ones. Linear programming is not suitable for that. I'd rather expect some variation on online scheduling (all the optimization algoritms are rather closely related though).

That's what I thought. But I found plenty of research papers talking about linear programming techniques applied to air traffic management.

Honestly this question is probably a bit to specific/technical, unless if you could get people who actually designed the software that's used, it'd be hard to give details, since most people that use the software just use it or press the buttons to get the result they need. In the US when flow times are issued, they're all done via computer(In the US, EDCTs are off Proposed departure time, APREQ programs are call the TMU when they're close to ready to go, and figure out a release time that works)

Linear programming (LP) is an optimization method that finds the highest (or lowest) possible value of a set of linear equations given a number of linear constraints.
There are a number of objectives in Air Traffic Management that may be described by linear equations. Runway throughput for example: twice as many aircraft can be seen as "twice as good". Or delay: one minute of delay of a passenger aircraft with 400 passengers is as bad as 2 minutes of delay for a passenger aircraft with 200 passengers (both have 400 passenger-minutes-of-delay). Mathematical models based on these linear relationship can help to make decisions for air traffic controllers/planners.
There are obvious limitations to linear programming. Not everything can be modeled as a linear relationship. Often the relations are more complex and linear models will be a poor fit because the relationship is not linear at all. In ATFM modelling, usually binary integer variables are used that can only take values of zero or one, thus a Binary Integer Linear Program is solved (BIP). And is 40 minutes of delay of a 10 passenger aircraft as bad as 1 minute of delay of a 400 passenger aircraft? These kind of relationships tend to prevent the small aircraft from ever taking off: it always pays off to let a bigger aircraft jump the queue. Perhaps a quadratic component in the  'cost-function' would bring a solution here.
Therefore more advanced models are needed. Methods like Integer Linear Programming (ILP), Mixed Integer Linear Programming, Mixed Integer Quadratic Programming and more advance optimization algorithms are used as well.
Another problem is that while these optimization methods may be able to find a best possible strategy, they are not necessarily easy to understand. Air traffic controllers don't like to be just told what to do, they need to understand why a strategy is proposed so they can think ahead and create what-if scenarios. It is impossible to program every what-if scenario in the optimization model, so at times the controller will need to deviate from the proposed solution. Without understanding what the algorithm had planned, it is difficult for a controller to predict the knock-on effects of his deviation from the proposed plan.
Early arrival management software worked reasonably well when the weather was nicely playing along, but gave hopelessly wrong suggestions when a couple of thunderstorms would render the normal approach routes unusable. Flexibility and two way communication between the system and the controller is essential to make a good product, there is much more to it than choosing the right optimization algorithm.

Even the linearity assumption that delay minutes per person is a good metric is something of a simplification. It's probably better overall to delay a large plane than a small one because the large plane is likely to be flying a longer route (more opportunity to make up the lost time) and also be flying fewer legs in the day (less susceptible to accumulating delays). So the whole thing is pretty non-linear.

@DeltaLima Excellent answer. That's what I was expecting about linear relationships. Thank you so much it helped a lot.

In Europe, the Network Management uses the Computer-Assisted-Slot-Allocation (CASA) algorithm in the Enhanced Tactical Flow Management System to allocate the departure slots. The CASA algorithm is a heuristic that follows the 'first-planned-first-served' principle and shifts departure timeslots of flights that would otherwise violate sector capacities. Eurocontrol describes the CASA Algorithm in the Air Traffic Flow and Capacity Management Users Manual:

In accordance with the principle of ‘First Planned - First Served’ the
system extracts all the flights entering the specified airspace and
sequences them in the order they would have arrived at the airspace in
the absence of any restriction.
...
In addition to this fundamental process, a number of other mechanisms
will act to compensate for factors such as late received flight plans
and modifications.

This is not the same as Linear Optimization.

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What is the procedure to fill/send/approve a flight plan to the ATS network from outside?
We are planning to develop an app that allows general pilots to fill/send a flight plan to the ATS. We're wondering to know if it is needed to have a regular access (register access or account) to the ATS network (thru AMHS or other way).
The idea is to automate the process through an app for general pilots.
For example, Garmin Pilot's app works and offers same solution., among many other related solutions for pilots.

I think you may rephrase to indicate that you want to know what is the current procedure to send/approve a flight plan so that you can automate through a software you are developing.

As far as I know, AMHS supports the filing of flight plans, but AFTN only supports doing that for military users.

thank @ManuH Actually you are right, it seems more accurate but on the other hand what I am also looking for is for web systems or external providers well known that could allow us to do this.

@JuanJimenez as far as I understand as AMHS is currently the standard for ATS messaging; my focus point is how to send information to this network (AKA "getting access") in order to fill/send/get approval for a flight  plan

@Carlos please, edit your question to make it clear at first reading (add precision and concision)

Using EUROCONTROLs „business-to-business web services“ you can file and manage flight Plans (including IFPS validation) as well as check details about the filed flights e.g. departure and arrival messages or where the aircraft is currently.
After a registration (you have to proof you are eligible to use the service) you do not need any ATFM connection at all - you implement the API features of B2B services into your app and that‘s it.
For more details and the conditions check: https://www.eurocontrol.int/service/network-manager-business-business-b2b-web-services

Appreciated to your response.


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At what distance between two aircraft will the air traffic controller get an alarm?
I am developing an air traffic control radar simulation.
At what minimum distance between two aircraft in mid-air should a conflict alert be given?

The first part is a duplicate of http://aviation.stackexchange.com/questions/2806/how-much-is-the-minimum-safe-distance-between-two-planes-in-flight

@ratchetfreak Yup, I linked to it in my reply as well. I have not voted to close though.

@Muzaffer What kind of ATC simulation are you building? Stand-alone game/sim or as a plugin to a simulator? You might want to google for VATSIM's EuroScope, vDSR or VRC clients to get some ideas and information.

@SentryRaven Plugin to a simulator.
I have downloaded and been using VRC client.
Thanks for your advice.
I am trying to build a radar which meets general standards. But I think it depends on airports.

EuroScope and VRC are adjustable to the needs of the vACC and vARTCC that use the clients. Quite a challenge you have set yourself. :)

Actually when I show product to client, I think he will change many of things as he needs. :)
So now, I just need some standards. Customization is not very important now.

The STCA (Short Term Conflict Alert) or pre-alert settings depend on the radar client in use and the ACC's or ARTCC's own standard operation procedures. Some ATC systems give a warning before a loss of separation can occur if criteria are met, informing the controller of a possible conflict. Factors can be clearing aircraft on the same altitude / flight level, aircraft on converging flight profiles, lateral or vertical separation reducing below threshold values, e.g. where 5nm lateral separation is required, a STCA could be set to occur at 7nm lateral separation.

The minimum radar separation between aircraft depends on airspace (TMA area vs enroute area), aircraft equipment and airspace separation requirements (RVSM vs CVSM), flight rules (e.g. IFR to VFR is not separated outside class C airspace in Germany) or local rules imposed by the Civil Aviation Authority.
The general rule of thumb for IFR separation in most countries (as most countries follow RVSM rules):

5nm lateral separation enroute (upper airspace)
3nm lateral separation in TMA area (lower airspace)
1.000ft vertical separation in lower and upper airspace where RVSM is observed and aircraft equipped
2.000ft vertical separation in non-RVSM airspace or between aircraft not equipped for RVSM

Oceanic separation is achieved differently, as non-radar procedures are in place. The separation in non-radar environments is achieved procedurally and through position reports and timing.

There are two main systems like the one you describe in use today: Medium Term Conflict Detection (MTCD) and Short Term Conflict Alert (STCA).
Common for both of them is that they do not provide an alarm when there is a certain, fixed distance between two aircraft.
Both systems rely on advanced data processing and 4D-trajectory calculations to estimate the future position of aircraft. If these calculations detect a future conflict, the systems will be triggered.
The systems will provide a warning to the controller, when a loss of separation (LOS) is expected to occur between two aircraft at some point in the future. The STCA will usually be triggered when the system calculates that the minimum separation between two aircraft will be violated within 2 minutes. For MTCD, this time frame is much larger, up to 20 minutes. The important thing to note is that the warning does not go off x minutes before the aircraft are going to hit eachother; rather, it goes off x minutes before the legal minimum separation will no longer exist. The warnings are designed like this, so that the controller will have time to solve the conflict before the minimum separation is violated.
As for the specific times used before a warning is triggered, it varies from system to system - and it varies within the same system too. In a busy TMA environment where planes are generally close and also flying at slow speed, meaning they are quite maneuverable, an STCA will go off much later compared to an ACC environment, where planes are generally further apart, and moving at higher speeds.
Modern ATM systems are simply so complex that there is no simple answer to your question.


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Can autothrust keep the plane aligned with the runway during crabbing?
I'm not talking about the entire auto pilot system, but only the thrust. Because I think, when experiencing crosswind during landing, the speed of wind may fluctuate and on 3 digit approach altitudes and below, it is hard for pilots to balance the forces with counter-forces without missing the runway. Is auto thrust precise enough to balance those forces in such short distances and short amount of time, and keep the plane aligned with runway after pilot points the plane against the wind?

Perhaps a small drawing of what forces you mean could help. I interpreted your question as "While maintaining constant crabbing angle w.r.t. the runway, is thrust variation from auto-thrust used to maintain a straight ground track?"; @kevin's answer has a different interpretation but I can't see from the question which interpretation is correct.

@Sanchises i've added a little sketch, it may help you understand. sorry if  the words i picked are not the exact name of forces , hope you get it.

I would have my doubt that it can, considering that engine response is not instantaneous.

EDIT: I take your question as "when crabbing the aircraft for landing in strong crosswind, is the auto-thrust precise enough to maintain horizontal alignment with the extended runway centerline?"
No. Auto-thrust is not precise nor responsive enough for this capability. Furthermore, auto-thrust is not used in this manner. To track the extended runway centerline when the crosswind changes, the pilots would increase or decrease the crab angle using rudder inputs.
Let us for a moment consider using auto-thrust to track the centerline. As an example, imagine an aircraft landing on runway 36 (pointed North) with a strong crosswind blowing East to West. The plane's heading will be somewhere between 360 and 90 degrees, while its track is 360. Suddenly, the crosswind increases, and the plane experiences a deviation to its left.

The plane is drifting to its left because the velocity component in the East-West direction is nonzero. If this is countered by increasing engine power, the plane can, theoretically, increase its velocity component pointing towards the East and get back on track. The problem is, flying a plane is three-dimensional! If engine power is increased, airspeed will increase, lift will increase, and the plane will drift above the glide slope vertically.
The correct response is this case is to input right rudder. Staying on localizer and glide slope requires frequent, precise but small changes. The right tool for that is the control surfaces. When using the crab technique in a crosswind landing:

Elevator is used adjust the plane's vertical speed
Rudder is used to adjust the plane's crab angle
Ailerons are used to maintain the wings level (to counter the aircraft's tendency to bank when using rudder)
Thrust is used to maintain airspeed (which keeps the plane from stalling)

From your question, it appears that you may have some misconceptions.
Thrust is forward. It controls the airspeed, which is also related to the angle of attack. Crosswind is wind blowing either left-to-right or right-to-left. Therefore, thrust and crosswind are unrelated; auto-thrust will not compensate for crosswind because thrust can only make the plane go faster/slower or go up/down, but crosswind blows side to side.
If your question is whether the autopilot uses asymmetrical thrust to control the plane in these conditions, then the answer is no: thrust is not responsive enough to control a plane's attitude, asymmetrical thrust is only used in emergency situations when no other options are available.
My bet is you're asking about gusts and wind shear, which can be experienced as either a headwind, tailwind or crosswind, so it may affect an aircraft's airspeed. Wind shear is defined as a sudden change of wind speed and/or wind direction.
The calculated speed of a landing is called Vref. In a normal landing, the pilots usually input Vref+5 into the autopilot. In gusty conditions, the pilots may input Vref+10 into the autopilot. A less flap setting may also be selected, again for the purpose of flying the approach at a higher airspeed. A higher airspeed is desired because it increases the stall margin.

When using the autothrottle, position command speed to VREF + 5 knots.
  Sufficient wind and gust protection is available with the autothrottle
  connected because the autothrottle is designed to adjust thrust
  rapidly when the airspeed drops below command speed while reducing
  thrust slowly when the airspeed exceeds command speed. In turbulence,
  the result is that average thrust is higher than necessary to maintain
  command speed. This results in an average speed exceeding command
  speed.
If a manual landing is planned with the autothrottle connected
  in gusty or high wind conditions, consider positioning the command
  speed to VREF + 10 knots. This helps protect against a sudden loss of
  airspeed during the flare.

quote from Boeing 777 Flight Crew Training Manual
Auto-thrust itself is precise enough to handle gusty winds to an extent, but it has its limitations. IIRC using auto-thrust is recommended in these scenarios, as it reduces the pilots' workload in a challenging situation. Plane manufacturers and airline companies often have limitations regarding the maximum gust / maximum crosswind. Attempting a landing outside these limitations may exceed the auto-thrust's capability to respond to rapid airspeed changes; it may also exceed the landing gear's strength or the wing's loading and therefore is dangerous.

I will read the entire answer but , let me correct something about first paragraph , maybe i wasn't clear enough, i know thrust has nothing to do with crosswind itself , please reconsider my question thinking after pilot points the aircraft against the wind.

@myhrra In that case, you may want to edit the question / reword part of it for better clarity.

@kevin. Are you sure this doesn't answer your Q? It says that autothrust is used to control airspeed, not groundspeed, not track, not heading.

@Federico I think my new answer should address this interpretation of the question; do you agree, or is there another interpretation?

Are you sure rudder is used to determine crabbing angle? I thought that rudder is only used on short final to de-crab (or to land in a sideslip if desired), or to prevent sideslip further out.

@Sanchises rudder gives the quickest response in a challenging scenario. If you bank using ailerons, you have to wait for the aircraft to bank, wait for it to turn, then level the wings. Remember we are talking about very small changes here, not using the rudder to turn 45 degrees (which is highly discouraged).

Fair enough. Thanks for the comment.

@kevin now we are talking , thanks for the answer

From your question, it seems that you have the following situation:
An aircraft is having a constant angle w.r.t. the runway to compensate for a crosswind. When this crosswind increases, the aircraft will as a result drift off the centerline of the runway. To compensate this, you imagine the aircraft speeding up to 'catch' the centerline.
Note that I'm not talking about 'forces' - it is helpful to think in velocities only when thinking about crosswinds, and assume the aircraft responds instantly so it only has a forward velocity relative to the wind.
Now, while this is in theory a way to deal with crosswinds, it's far from ideal. Much better is to simply change your crabbing angle, so that the sideways velocity component (w.r.t. the runway centerline) matches the crosswind. This is much quicker, although it does mean banking is required. You will see that, when the changes in crosswind become too sudden on short final, a go around will be necessary to avoid excessive banking near the ground. Airspeed is kept constant with auto-thrust, not 'crabbing speed'.
From a automation perspective, your suggested way of dealing with crosswinds is entirely possible - an aircraft is capable to detect its lateral and angular deviation from the centerline, and could calculate thrust accordingly. However, physically, a jet engine needs time to spool up to produce the thrust required, and spool down before less thrust can be produced (there is a lot of inertia, and the combustion chamber does not have very relaxed margins as to suddenly injecting extra or removing all fuel).
Furthermore, the airspeed will fluctuate, requiring different angle of attack continuously, and possibly excess velocity on touchdown. Note that when the initial crabbing angle is very small (say, a 1kt crosswind), you would require ludicrous amounts of speed to account for a small increase (the extra speed required varies inversely proportional with the crabbing angle). Conversely, when the initial angle is quite large, you would need to stop in mid-air when the crosswind dies down. All in all, a simple bank to change the crabbing angle is a much more effective way of dealing with a crosswind.

yes, I think that this is more in line with what the OP was asking

@Federico I see that kevin just amended his answer, too, so I guess the OP now has two answers to choose from :)

another good answer , thanks @Sanchises

The question was not whether the autothrust/autothrottle DOES keep the aircraft aligned, but whether or not it CAN keep aircraft aligned. There is a very interesting, but not well known story that took place after United Airlines Flight 232 crashed in Sioux City in 1989.
After having lost all hydraulic power on a DC-10 aircraft due to a failed disc on the #2 engine which severed all the hydraulic lines, Captain Al Haynes, First Officer William R. Records, Second Officer Dudley J. Dvorak, and some random check airman who happened to be on board to offer his assistance, Dennis E. Fitch, managed to cohesively work together to guide the aircraft to Sioux City. Although the plane crashed, they exclusively used the remaining engines (engines 1 and 3) to get the aircraft there. Although many lives were lost, many were also saved.
Following that, an engineer at NASA came up with the idea to implement a sort of reversionary mode of the autopilot/autothrottle systems that could safely perform an auto land with all hydraulic power lost. Although never implemented, it was successfully tested on an F-16 and then on a passenger version of an MD-11 and B747. The story, an excellent one to read, is chronicled here. Although it includes many technical details, even further technical information can be found here.
This is a video of the F-15 demonstration. There is actually a video of the MD-11 performing a landing, but I can't seem to find it.
So, to answer your question. Is the auto throttle capable of everything you asked? Absolutely! Is it installed/implemented on aircraft? No.

Note that the method you describe actually does use differential thrust to induce rolling etc., so it is a bit different from what the question asks. Also, I doubt that the system will handle gusts on short final - but who knows.


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What safeguards are there against unintended inputs?
A modern passenger jet suddenly encounters some very turbulent air. The captain, who was just enjoying his toilet break, rushes back into the cockpit. Just as he's about to sit down the plane drops, causing him to hit his head on the overhead panel, accidentally pressing some buttons with it. Oops...
Does this happen and how is the potential impact mitigated?
Are the buttons in the cockpit designed to withstand accidental activation from such uncontrolled movements? Do they activate instantaneously or require prolonged pressure?
If activated immediately, what are the most dangerous buttons, and do the pilots have enough time to assess what happened and undo some of the changes before they present a real danger?
What about other types of accidental inputs? For instance, a pilot stumbling and inadvertently interacting with the center console controls, or any other plausible scenario that has either occurred in the past or could reasonably transpire in the future. How are these potential incidents managed within the cockpit's design?

A video about an incident where the pilot's camera was wedged between the seat and the yoke, causing unintentional input: https://www.youtube.com/watch?v=Dl-Fl66Jfao

The buttons activating functions that cannot be cancelled are protected against accidental activation

Some buttons have a guard cover that has to be opened before you can reach the switch. You won't open that by just bumping into the switch.
Engine fire extinguishers usually need to be pulled and rotated. Again, won't happen by just bumping into them.

These also protect against activation by accidentally reaching for the wrong switch by being very different from the simple buttons or flip switches around them.
Also rotary switches are somewhat safer against this since they need to be grabbed rather than just pushed.
But otherwise no, most switches are not protected against accidentally bumping into them.
And it did cause some close calls and even accidents in the past. One example that comes to mind is Gol flight 1907 which was caused by the pilot of the other plane involved accidentally—not even any turbulence, just somewhat careless placement of leg and less then ergonomic placement of the switch—turned off transponder (and less then ergonomic radar display due to which the controller didn't realize anything is wrong and therefore didn't query the pilot what is going on).

There aren't any switches on an overhead panel that will cause the airplane to do anything crazy from random bumps by a body part. It's all subsystem on/off or mode switches. The more important subsystem switches, say for the main generators, are normally the "lever-locked" type; that is, you have to pull them out to select them, and bumping them with your head without doing that will just leave a dent in your head.


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What can happen if a bird strikes the engine during landing?
I am not sure what can happen if a bird strikes an engine during landing.
To narrow it down: commercial airliner (B787/A380 etc.) hitting a large bird so engine out is likely.

There are many phases for landing. If you are over the runway and flaring you may continue the landing.

If you are over the runway and happen to be the bird, you might consider getting out of the way...

What kind of aircraft? Commercial? General Aviation? Most engines are at flight idle or very low power during landing. Depending on where you are in the landing phase this is either a issue, or not so much. Hitting a bird at 1500 feet on a 5 mile final which causes your engine to quit is a big problem. Hitting a bird at 50 feet over the threshold might cause your engine to quit, but the runway is right there...

The bird will die.

Seriously? Why the VTC? Are the there really that many possible outcomes that it's too broad? I can only think of 3 - land anyway, go around or crash. Yes it depends on the phase of landing but I think it's reasonable for an answer to cover the various phases like the current answer does.

If you're a single engine pilot asking I have an answer.  If you're a concerned airline passenger I don't have an answer except that I'd trust the airline.

I will talk from my experience as an A7E light attack pilot. It was always a frightening experience at any stage of flight. We had a turbofan engine, which is usually more forgiving to foreign object damage, or FOD, but nonetheless taking a bird of any size in the intake would almost certainly cause an engine failure. And taking a bird hit through the canopy wasn't  much better. So, it can be a catastrophic event in certain aircraft, while rather benign in others.
Was in the front seat taking off on a training hop, and had wheels in the well, when we passed through a large flock of birds at the end of the runway. We were at around 500 feet AGL. It was mesmerizing. As you approach a bird that is above you it will instinctively tuck its wings and dive to get out of your way. So as we flew through the flock there were birds co-altitude with us veering left and right and then the birds above us diving close past the canopy. Miraculously we were not hit.
The other experience I have with a bird strike was when I was in the fleet rolling in on the target. I was in a tight right-hand descending turn. I was clearing the left side of the aircraft, looking over the canopy rail when I saw a speck on the canopy. I remember thinking that, "Hey the plane captains are usually better than that at cleaning the canopy," and then the speck turned into a Turkey Vulture. It impacted the fuselage a few feet behind the intake in the gun port. Luckily for me I was on a NATOPS Safety check flight and so was able to demonstrate my knowledge of a precautionary approach.
The ordinance men who fixed the gun were not happy with me. They said the repair was quite messy.

A range of things can happen.
For an airliner with a modern turbofan engine, the mostly common outcome is, absolutely nothing happens to the aircraft (although the bird's day is pretty thoroughly ruined). A sparrow can be chopped up by the fan blades & blown out the back, and the crew will never notice it.  The engine won't hiccup, and until somebody sees a trace of blood and feathers on the fan blade during a walk-around, nobody will have any idea it happened.
Next case is a small bird gets ingested into the core. Chances are good the engine will keep running (remember, small bird we're talking about here), although the crew may notice a fluctuation in the engine instruments and there may be the smell of cooked (charred) bird in the air conditioning system.
In both of these cases, the engine will be inspected; the case where the bird went into the core takes longer, because maintenance will have to use a bore scope to look inside the core to inspect for damage.
The worse case than either of these is a big bird (or several) going into the engine.  Depending on the specifics, the engine may chop them up & spit them out without damage, or the fan blades may be damaged, and/or the core may be damaged, and in the bad case the engine loses power, and in the worst case, it quits.
Losing one engine to a birdstrike is quite rare and is a pretty big deal, but most certainly not unrecoverable. An airliner can fly fine with one engine shut down.
If the birdstrike happens on short final, the crew might simply use more power on the operating engine and continue on to land. If it happens farther out, they might continue or they might discontinue the approach, go around, shut down the damaged engine, and then come back and land.
The really, really bad case is where you get enough bird strikes that they shut down all engines, and at that point you're a glider.  If that happens at 50' over the runway, your only choice (land straight ahead) still gets you where you wanted to be anyway. If it happens farther out, well, that's where somebody gets to try to be Sully 2.0.  That sort of a scenario is extremely rare – like one in tens (if not hundreds) of millions of cases rare.
You're far more likely to get hit by a semi truck driving home from the airport than having your day ruined by a bird going through an engine.

well it's not that rare, it happened 2 times in 10 years. (US airways 1549 and Ural airlines 178), and in both cases they were extremely lucky. I wouldn't describe a potential loss of 150+ passengers every 10 year as 'extremely' rare accident

@user2591935 That's two times in what, 40 million or more flights? From the perspective of "per flight," that's pretty rare. The news viewer sees 2 in 10 years that one happened; the engineer sees 39,999,998 flights that it didn't.


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Is the Fortran language still being used in aviation?
I am an aeronautical engineering student at Istanbul Technical University and our course plan includes Fortran as a programming language. I have some doubts about that because Fortran is an old language.
Is Fortran still being used in aviation?

Hi.  Welcome to Aviation.SE.  If you are learning how to write code, then your question is the wrong one.  You are better asking this question on Programmers.SE to understand why.

Not directly about aviation, but I have friends who run simulations written in Fortran on US Government super computers. They learned Fortean specifically for this purpose in the last few years. The mathematical and parallelization libraries for Fortran are very good and very efficient so if you just want to do a lot of math on lots of processors Fortran is still a good choice.

The last stable release of Fortran was in 2008, and considering the language itself is almost 60 years old I wouldn't classify it as an "old" language, but a mature one. Granted it isn't used mainstream anymore, but for mathematical analysis Fortran is a very good language to know.

Related if not duplicate...

You will learn "Programming". The language is not important (yet).

Given how old and outdated Fortran is, I expect it is used extensively in the aviation industry.

@JonathanWalters If you think Fortran 2008 (or the upcoming 2015 version) are "outdated", most likely you don't actually know Fortran. You do realize that standard Fortran now supports object-oriented programming, parallel computing, etc, etc? Admittedly, there are lots of people still writing code that looks pretty much the same as Fortran 66 used to, but that's not the fault of the language.

@alephzero: "standard Fortran now supports object-oriented programming"  Which is perhaps a good reason NOT to use it in aviation.

@mins: Not only that, but from what I understand, the people maintaining the standards for those languages are more interested in expanding the range of things the language can do, unlike those in charge of the C Standard who in the name of "optimization" have reduced its ability to do things that FORTRAN can't.

@jamesqf I don't see any reason why an object-oriented language couldn't be used in aviation. Compare and contrast C++, which is a multi-paradigm language that can be used in an object-oriented fashion. I'll grant that in some situations in aviation programming, you definitely would not want unpredictable execution which is an argument for using a non-garbage-collected language and runtime, not a non-object-oriented language. In other situations, I suspect being able to succintly and readably express what you want the computer to do is more important than the exact execution time.

@GiacomoCatenazzi: which languages you use when learning programming is very important. Not only they help you to structure your thoughts, differently for each approach but also help you to learn new ones. FORTRAN is probably (with BASIC) one of the worst to start with. As a side note, I have a PhD in Physics where FORTRAN was the language of choice and it was a true nightmare compared to even C. Like my excellent professor used to say "I like to keep my 10000 lines of code in one file to have everything handy, neatly in one column". FORTRAN might have changed, though (but what for?)

@WoJ: Try RPG, you'll love Fortran and adopt Basic.

FORTRAN is not used much that I'm aware of in aviation, but it is significantly used in aeronautical engineering.  I work with people that use Mark Drela's 'xfoil', 'xrotor' and 'aswing' programs on a daily basis for the design and analysis of airfoils, propellers and aerostructures. And I've used the 'CHARM' model of rotorcraft dynamics.  All of these are written in FORTRAN and you often need to know the language to debug them or integrate them into other programs e.g. for global design optimization.

It Fortran, not FORTRAN. For more than 25 years it has been.

@VladimirF depends on its revision I guess... FORTRAN 66 and FORTRAN 77 are named in caps.

@Ruslan '77 goes back to 1977-1978 says Wikipedia, dating it to a conservative 37 years ago. I don't see how that contradicts Vladimir F's comment.

@MichaelKjörling my point is that there may still be in use programs written in those old versions of the language.

NASTRAN, frequently used for FEA (Finite Element Analysis) in aerospace applications is written in FORTRAN and apparently skilled practitioners have to delve in at a low level in some serious applications.

Fokker Services and DynamicSource AB
  have jointly developed an iOS Application to run
  FORTRAN Take Off and Landing SCAP (Standard Computerised Airplane Performance) modules on the Apple iPad®. The app allows an operator to make the performance  calculations shortly before take-off and therefore allows the opportunity to incorporate last minute changes with respect to aircraft loading and runway conditions.
OEM take-off and landing performance calculation modules are complying with the IATA SCAP interface specification. They are written in Fortran. Normally Fortran programs do not run on iPad® , but the software engineers from DynamicSource AB managed to  make this possible.
The OEM-supplied SCAP module is combined with a calling program and an airport/obstacle database. Via a user-friendly Graphical User Interface (GUI) relevant data like aircraft-weight, wind, and runway condition are fed into the app. Within seconds the take-off and landing data like V1, V2 and flap setting are presented on the screen of the iPad®.

Fortran at 59
Notes for "Fortran at 59

FORTRAN is still in active use for AT LEAST the following reasons, not all of which I have seen spelled out here:

FORTRAN has a huge legacy base of code that just works and has stood the test of time.  Sure, you can pipe the source through a FORTRAN-to-C converter (which is how some modern FORTRAN compilers actually work behind the scenes), but then you largely ruin any self-documenting nature of the code -- which for many programs and algorithms is the only documentation that exists or is complete and reliable.
The syntax and control flow of FORTRAN is relatively simple compared to many modern languages and thus can be used as the "lingua franca" for distributing calculation algorithms that demonstrably work.
As a corollary to the immediately preceding point, the fact that FORTRAN is a relatively "dead" language that will not be revised can be seen as a good thing.  If you publish a scientific finding, and include the FORTRAN source of the algorithms used to extract the critical data and perform the analyses that support the finding, there is no question that in 50 or even 100 years, scientists and researchers will still be able to run your code somewhere.  Can the same claim really be made for something like MATLAB? I think not.

You'd be crazy, of course, to try and write a GUI framework or really anything beyond pure number-crunching code in FORTRAN. But what it does, it still does very well.

the fact that FORTRAN is a relatively "dead" language that will not be revised WTF? Draft Fortran 2015 is already finished. (Fortran, not FORTRAN). Maybe you just meant that the backward compatibility will be maintained?

Yes, Fortran is still being used. However, don't get too worried if you find your class less than exciting: Most Aerospace engineers don't do much (if any) computer programming. However, if you intend to go on to graduate school, pay attention in you Fortran class!
I think your first priority (regardless of your grad school plans) should be Matlab. Everyone uses it today, especially if you publish. The power of Matlab (and Mathematica) is in their ability to do algebraic equation simplification and producing pretty (publish ready) output.  Mathematica used to be the king of the hill in this area, but Matlab has pretty much pushed them out (although Mathematica is seeing resurgence due to the free Raspberry pi version). These are both great tools, but if you need to crunch big data, the tools of choice in Aerospace are Fortran or c/c++.
Fortran is preferable when dealing with complex numbers and has many built-in vector, matrix, and mathematical functions. However, it falls short when trying to deal with pointers or interfacing with low level operating system functions (where c shines). But, only a small percentage of Aerospace engineers write code in these languages. Most of the Fortran at Boeing runs on their massively parallel machines performing electromagnetics and fluid dynamics calculations in research areas. The c languages are primarily used in embedded systems (avionics).
My recommendation: You should be proficient in Matlab but know you way around (be able to read and understand) both Fortran and c...

My current employer in the flight simulation industry still uses it on new work. We are trying to move away from it, but its simply not possible (or sensible) to do 100% when we have a lot of fully-debugged reusable code written in it, and we still occasionally get flight models from vendors that employ it. (That right there is your big huge clue that yes, the Aviation industry is still using it)
I believe most other major players in the flight simulation business are in the same boat. Even when we do move away from it, its mostly to other non-VM procedural compiled languages like C++, which I suspect a lot of college students also consider "old languages" these days.
Even if we could get rid of Fortran in all our new jobs, we have a lot of delivered systems that use it, and those periodically need bug fixes or upgrades (obsolescent hardware replacement efforts, etc.). So we would still have to support Fortran for another couple of decades.

I've been told directly by a director of UAV development for the U.S. that Fortran is still used in their UAVs.

While this may be true, this answer would be much more helpful with more detail or sources to support it.

All I have is a personal statement made to me. Just annecdotal evidence from late 2000s. http://www.acq.osd.mil/sts/organization/bio-weatherington.shtml

authors: Vladimir F Героям слава


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Is there any "copyright" for aircraft's design between different manufacturer?
Are there any regulations for the copyright of aircraft's model design between competitors in the aircraft industries? Basically is there a regulation for avoid that one company just steals the project of a competitor to produce a version very close to the original?

Sorry for my english, feel free to modify.

These idea about copying an aircraft's design came in my mind after seen the Sherpa 650t  which seems very close to a pc-6. I am not familiar with that aircraft and I obviously not suggesting that is the same at the pilatus but I am just saying that they look very similar one to another, so I got this idea. I hope that I explained myself clearly.

Similar requirements tend to lead to similar designs. Nothing to do with copyright laws, nor trademark. Any document is implicitly under copyright in most countries, so you can't make a photo copy of a design drawing without permission. That's all copyright law does.

This is more of a law issue rather than aviation issue. Anyway here it goes: No, there is no copyright to prevent one manufacturer from copying another aircraft because aircraft design is not protected by copyright.
The first rule about copyright is that it "protects an expression of an idea but not the idea itself". It protects technical diagrams, documents, recording etc, but not the idea expressed in them. Therefore if one simply photocopy the schematics, it would be a copyright violation. But if you reproduce what you see, it is legal.
The word you are probably looking for is "patent", which protects an idea. Aircraft manufacturers do have patents when they come up with something revolutionary. A quick search for "Airbus patent" turns up quite a few results. Whether you agree that particular idea was revolutionary enough for a patent though is another story.

Just take the Boeing 727 as an example which was targeted squarely at the Hawker-Siddeley Trident's market and succeeded in displacing it almost everywhere.

Within countries, you have patents that protect the work of one company from being taken by another. Between companies in different countries is a whole different mess to deal with as some of it depends on diplomatic relations.

Not sure if this constitutes a whole other answer, but in countries like the United States, projects that are top secret (Have Blue, Archangel, Oxcart, for starters) all have proprietary technologies that are prohibited from export, or even carrying over for projects for other agencies/military branches. In fact, this is the main reason the F-22 Raptor is not allowed to be sold even to longtime powerful allies of the US, such as Germany, South Korea, and the UK, although all three could definitely afford a considerable number of them. If this gives you a better idea of the situation.


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What does this black triangle placard on board an A320 denote?
Just out of interest whilst travelling aboard a British Airways A320-232 G-MIDT on the 9.45 BA shuttle service (LGW-GLA) in seat 10F I noticed a placard above the window  of seat 9F. Given this seat was two rows forward of an overwing exit I was wondering if it was related in any way.

From non authoritative sources online, it may indicate a window from where wing extensions (flaps, slats) are visible and can be checked visually (position and ice formation). Color is brown or black.

Hm, I am pretty sure I've already seen a question here about exactly the same marks in some other aircraft type. The search is not good enough to bring it up as related unfortunately.

On quora.com someone said “The black triangle marks the location of what has been called "William Shatner's Seat," the seat with the clearest view of the wing.”

This video has the answer to your question. Cheers.

If there is a problem on-board and the crew is unsure about the condition of the aircraft, the triangle indicates what window should be used to inspect flaps, slats or engines or look out for icing.
This saves important time in case of an emergency, as the crew doesn't has to search the right window to look out.
For example if there is a failure of the flaps condition display, it has to be verified visually that the flaps are extended properly. From the window with the triangle, this can be seen:

Source, added square
Now the crew can compare the position of the flaps switch in the cockpit, with the actual extension of the flaps.

There are usually four of these triangles in the cabin. One to inspect the forward of the wing for icing, the slats and the engine on each side and one at the back of the wing for the flaps.
I have searched for cabin pictures and found this 360° cabin view by SAS.
The following picture shows the triangle on an Airbus A330 at the front of the wing. You can see a part of the engine through the window.

Source, added squares
And this picture shows the rear triangle.

Source, added squares

But that sign looks like easily detachable. Any asshole can pry it off the plane. Also, are there similar signs in Boeing planes?

Yes, in Boeing planes it's the exact same sign. And yes, I agree, it looks like it's only a sticker. Maybe it's part of the flight attendants cabin inspection to verify all triangles are intact.

Yes, @Firee, it could be pried off, but doing so would be pretty obvious to the cabin crew during flight and to surrounding passengers during (un)loading. The CC, I'm sure, would put a quick stop to it in-flight, and probably request police presence at the gate upon landing. One would hope that other passengers would, if not directly intervene with someone tampering with the aircraft, at least report it to the CC prior to take-off or when disembarking. I know I'd say something to the crew.

Some decal adhesive is designed to be much more difficult to remove than typical decal adhesive.  I was thinking about the kind of decals that are used for asset tags on expensive equipment: they are quite difficult to remove (and tamper-evident).  If one really wanted to ensure that a decal stays in place, one could stick it down with epoxy and put a clear layer of epoxy over it as well.


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How do radio altimeter systems compensate for objects on the ground?
My understanding of a radio altimeter is that it can provide more accurate altitude readings below the transition level.
It occurred to me a number of days ago whilst sitting beneath the glide path at my local airport that surely discrepancies must arise when using radio altimeters due to objects such a parked vehicles and trees beneath the flight path of the aircraft.
Are these negligible or are they taken into account by the system or the crew?

Yes, they do measure to the nearest object.  (Assuming it's not something that is transparent to radar.)   Just as you say, it is negligible or taken in to account.

Objects on the ground are negligible because the radio altimeter is not designed nor used to such high precision.
There are several uses of the radio altimeter. The first one is for timing the flare during the last portion of the landing. Since the flare maneuver starts after the aircraft has crossed the runway threshold, at this time the aircraft is over flat ground.
The second usage is terrain awareness. The radio altimeter will trigger the GPWS "terrain! terrain! PULL UP" warning if the reading is too low. If you are in a range where the height of cars or trees matters, you are too low anyway.
You may imagine that pilots use the radio altimeter as their main data source for height above ground during the landing phase. That is not true - the barometric altimeter is always the primary instrument to use, until the flare portion at least. That is why pilots need to adjust the altimeter to the local air pressure setting. However, the radio altimeter can provide useful situation awareness. For example, you are landing at an airport with elevation 2,200 feet, you are 10 miles from the runway, and your altimeter reading is 3,800 feet. Suddenly you hear the automated voice "five hundred" in your cockpit. Needless to say something is wrong.
Pilots cross check the barometric altimeter with the radio altimeter during landing. The airport elevation is usually dialed-in somewhere on the cockpit display for quick lookup. When the automated "five hundred" announcement is made (or announced by the pilot not flying / flight engineer on an aircraft without automated announcement system), you quickly glance at the barometric altimeter to see it is 500 feet above airport elevation. It does not have to be exactly 500 - 492 or 518 will do as well. Then you cross check the distance to runway threshold with the DME (if available). Again, you don't have to be exactly 0.8 nautical miles or whatever distance the calculator come up with. As long as you're reasonably close, it is good enough.
If the pilots are using the ILS, then vertical guidance will be provided by the glideslope signal until decision height, at which point they will switch to the barometric altimeter again.

Also, a radar beam is not a laser; it will not measure a single spot: rather the signal will hit a section of the ground (the higher the transmitter, the larger the area it will hit), and the reflection will effectively be an average over that area.  Unless a truck or tree is absolutely massive, it will get averaged with the surrounding area and distort the readings a negligible amount.

I can believe that these days with better equipment and with pilots doing less hand flying than in my time, the answer is descriptive of current practice. However, in flying 747s at 2 carriers during the 1990s, that's not quite how we did it. Once in sight of the runway and below 1000 ft on the baro altimeter, we didn't use it as there was no need with the exception that the baro altimeter was used to call decision height when on an ILS. The first call of our old radio altimeters was 100 ft, although many of them weren't "talkers" in which case the f.e. made the call.

@abelenky, the radar performs a weighted average.  A strong reflector like the metal body of a truck will count for far more than a weak reflector such as a tree.

@abelenky because a (simple) detector circuit will detect a rise, there can also be a bias towards higher objects as they reflect first.  This can to some extent be tuned out so a single prominent object doesn't cause too much trouble, but of course we might want to know about prominent objects

Radio Altimeters may be classified based on their time measurement methods. Basically they are measuring time elapse between transmission and reception of signal. Here is a common diagram;

So if we take speed of light as a constant "c", height of the a/c = c * time elapse. Signal transmission and reception time is critical.
Most common radio altimeters works in 4.4 GHz level. Which means every 0.22 nanoseconds it transmits a signal.Can you imagine how many changes need to occur during a normal approach due to terrain changes?
In order to keep things simple and reasonable manufacturers add control units to Altitude Display and Altitude Alert functions. This control units gives you a "window" of altitude you are flying. If you are flying over the sea on a windy day and level of 1000ft. you do not see the effects of waves at your altimeter.
Based on manufacturers tolerance limit +- 10 ft or less is added to prevent over informing pilots.
If you are using pulsing radio altimeters with lower frequencies you will see measurement areas which means you do not measure all the terrain beneath you.There are missing parts but again negligible.
There are many researches going on for more precise radio altimeters especially for unmanned air vehicles. These new types covers more terrain data and maps for proper alerting system.
I believe we keep using those tolerant RAs for a while as airliners.
Cheers,

"Most common radio altimeters works in 4.4 GHz level. Which means every 0.22 nanoseconds it transmits a signal... " I believe this is wrong. 4,4 GHz is the frequency of the transmitted signal, not the PRF. (Pulse Repetition Frequency). It is the PRF that determines the time between pulses, not the signal carrier frequency. Plus, do the math, in 0.22 nanosec, the signal would travel 0.2160576 feet or 2 inches. If the radar was sending pulses that are 2 inches apart, how could it know which transmitted pulse an echo came from?


text:
How do planes search for submarines?
I am interested in the process of using maritime patrol aircraft in an antisubmarine role. I hope there is some general answer, because I have no idea what such missions look like.

How long can such a mission be and how big an area can it cover?
What techniques are used during such missions?

What is the context of the mission? Are the planes defending friendlies against submarines? Trying to scare them out of a specific area? Just trying to spot them for later strikes? The goal of the mission can affect many of the topics you're inquiring into.

Well, I hoped for some general answer. Should I divide the question into a a) in case there is no war and b) there is war?

I think this question is too broad, as it stands. Essentially, it boils down to, "Anti-submarine patrols: tell me everything about them, including how the weapons work." If you can edit your question to be more specific, it would be a better fit for the site. Breaking it into two or three separate questions might also be better: you can provide hyperlinks between the questions if needed for context.

One way is to drop multiple sonar buoys across an area to triangulate returns. Hunt.

Update. Added: much more informative P-8 diagram, sonobuoy diagram, ASW training film (see bottom), ESM, minor formatting fixes. Removed: consolidated two sonobuoy loading pics (linked but not shown inline).

This principle method of airborne sub-hunting is using sonar to search a wide area around your ships in the direction of advance. The intent is less tracking subs as it is to deter them from getting into a good position to shoot and/or obtaining a firing solution on your ships.
ASW is a long, complex topic (see bottom for USN training film). This answer will be brief unless someone has more questions.
Airborne sensors include:
Sonobuoys

Passive - (omnidirectional or directional) - subs are very quiet today. Detection ranges is extremely short. <100 m by some accounts.
Active - all subs are coated with anechoic tiles to absorb acoustic energy
A P-3 would go through about 10-30 buoys over a 6-10 hour mission
A P-8 can apparently cary 120 sonobuoys.
Some vendor specs are available.
GREAT video of sonobuoy deployment. (This is one type. Not all are this complex.)

Source. Illustrator.

Alternate view #1. Alternate view #2. Credit.
Dipping sonar
Unique to ASW helos

Credit: USN
MAD - magnetic anomaly detector
The large boom extending behind the tail:

Credit: DoD

looks for large metallic masses
limitations: short range (100s of meters), which requires aircraft to fly very low over the surface (increasing airframe fatigue and fuel consumption). Descending from cruising altitude also takes time.
upside: good localization (spatial accuracy), relatively few false positives.
downsides: Equipment is large and heavy. For these reasons, a MAD boom is not included on the current USN P-8, the navy's newest long range maritime patrol aircraft.
Counter-measures:

Sub can dive deeper to reduce their chances of being detected. Typical SSN operating depths are 400 m. The Type 214 claims a 700 m test depth.
Some modern subs are made from non-magnetic steels (eg, German Type 212, Type 214) or titanium (Soviet Sierra, Alfa, and Papa class SSNs, portions of the Typhoon's 5 pressure hulls).
Subs also undergo degaussing

LA-class USS Toledo (SSN-769) prepares to get underway after four days at the Magnetic Silencing Facility. 5 Feb 2010. Credit: USN

Radar

Historically, more useful for detecting subs on the surface, forcing them to spend more time underwater, where they were less effective (slower, limited endurance, limited sensor range). For much of WWII, German U-boats were essentially submersible torpedo boats. Most of their attacks were actually made on the surface.
Today, our improved radars can detect submarine periscopes (and their wakes) at significant distances, forcing subs to take only very short glimpses. The periscope is actually quite useful for ID-ing targets and obtaining ranges and headings much more quickly than stalking with sonar alone.

Signal intercept, ESM
You may detect a sub communicating over radio. You may also detect a sub if it uses its radar (very seldomly).
Visual
If you're directly above a sub at shallow depth, you can see it. Needless to say, this is extremely rare, but is one reason operating in shallow, littoral waters is dangerous. If you're lucky, you might spot a periscope wake. It's also unlikely you'll see a surface wake. At periscope depth, subs move very slowly. And at operating depths, surface wakes are extremely minute, likely undetectable even by radar and advanced processing, although attempts have been made.

Credit
EO/IR
General SA but may occasionally detect exhaust fumes (eg SSK snorkeling) or periscopes/wakes.
Other non-acoustic methods

Chemical (eg hydrocarbon sensor) - to detect snorkeling subs recharging their batteries
LIDAR - potentially faster than MAD. Limited depth and search band. Less effective in turbid coastal waters. Not used operationally.
Radar to detect the minute thermals from warm water heated by reactors. (Claimed by Russians, not demonstrated by US.)

Examples
Land-based maritime patrol aircraft examples: P-3 Orion (modded L-188 Electra), P-8 Poseidon, ,
P-8 Poseidon (modded 737-800ERX).

The Boeing 737 Technical Site. Source page with lots more info.
BAE Nimrod (based on the de Havilland Comet)

Source
Carrier based platforms include: S-3 Viking, SH-60 Seahawk
SH-60 Seahawk - sensors includes a variable-depth active/passive sonar, sonobuoys, and MAD.

MAD bird (orange/red). Credit: DoD
Anti-submarine warfare intro
COORDINATED ASW PART 1 - Coordinated Anti-Submarine Warfare 2089 (HD version below)

And of course the mark 1 eyeball, if a sub is to near the surface it leaves a wake.  Not a certain sign but a good trigger for looking harder.

@Hephaestus Thanks for the answer! I'v got some explanation also here

authors: Александр Кишкель


text:
Can the use of flaps reduce the steady-state turn radius at a given airspeed and angle of bank?
Note that for the purposes of this question, I am only interested in the scenario described below. By 'steady-state' I mean to exclude from consideration the short-term effects of changing the flap setting during a turn.
In the YouTube video Should I Use Flaps in a Turn?, beginning at 10:59, there is a claim that, at a given airspeed and bank angle, having the flaps lowered will decrease the turn radius. This is followed by a demonstration in a PA-28 where airspeed, bank angle and height are being held as constant as possible (70 kts, 30 degrees and 2,000 feet respectively) through two 360-degree turns: firstly with flaps up and secondly with 25 degrees of flap. It looks pretty convincing if we assume the bank angle and speed were adequately matched in both cases (though there are some variations apparent in those shots showing the panel and forward view during these turns).
The explanation given is this: "The turn radius of an aircraft is directly related to the horizontal component of lift which, as you may remember, is how we get an aircraft to turn. Well, what do flaps do? Yes, they increase our drag but they also increase the amount of lift that our wings produce, so instead of increasing our bank angle (which increases our load factor) we can just lower more flaps. This allows us to tighten those turns up."
The doubt I have over this explanation is that, while (at least in the normal flight regime) lowering the flaps increases the lift at a given airspeed, air density and angle of attack, what's being held constant throughout these tests are airspeed, air density, and the requirement for the vertical component of the lift to be equal to the weight (this last constraint is on account of these tests being conducted at constant altitude, so there is no vertical acceleration).
Given that both tests are performed at the same bank angle, however, this last constraint on the vertical component of lift means that the total lift would be the same in each test, and the same can be said for its horizontal component. It is the latter which acts as the centripetal force for the turn, and the only other variable in determining the radius of the turn is the speed, but that is also the same in both tests.
If this phenomenon is real, what am I missing or getting wrong in this analysis, and how do we calculate or estimate the size of the effect?

You answered the question yourself in the second-to-last paragraph--

Well, I thought I had!

No.

... claim that, at a given airspeed and bank angle, having the flaps lowered will decrease the turn radius.

This claim is nonsense. For a coordinated turn, bank angle and speed alone are sufficient to determine radius. This can be derived from basic physics. The equation is:
$$ r = \frac{v^2}{g \times \tan(\theta)} $$
Where $r$ is the turn radius, $v$ is the speed, $\theta$ is the bank angle and $g$ is the acceleration due to gravity.
Note that shape of the airplane is not a variable in that equation. Physics don't care if flaps are extended or not, or if the plane even has flaps, or if it's even a plane at all.
The argument about flaps is based around the fact that they permit lower airspeeds without stalling (at the cost of increased drag). But that's not the claim in your question.

It's possible that a given aircraft has a different indicated airspeed for the same calibrated airspeed when the flaps are up and down. So this could appear to be the case, I suppose, although in fact the actual explanation would be that the airspeeds are not the same in the two cases.

@Chris-RegenerateResponse Good point! In this PA-28 140 manual it says at 70 mph IAS, CAS is 75 mph flaps up and 72 mph with 40° flaps (at 80 mph IAS they are 83 mph and 81 mph respectively.) This is in the right direction and turn radius goes with the square of the speed, but it does not seem to account for the all difference in the circles, plus only 25° flaps were used. (OTOH, the forward-looking shots from the cabin and the non-circular 'circles' show there was some variation in the flying.)

@sdenham there may also have been variation in the wind. It's really hard to test something like this in flight!

Slightly nitpicky, but in the response it says that physics don't care " it's even a plane at all". In strict interpretation that's true of course, but the formula given assumes in its deduction that we're dealing with something that flies and can point its lift vector by banking (yes, rotary aircraft, and yes you could use the same formula to find by how much you need to "bank" train tracks to run through without lateral acceleration being felt). I guess my point is the assumptions put into the physics models to arrive at a formula shouldn't be dismissed in an offhand remark by accident.


text:
How do I interpret these Center of Gravity limits?
In the normal category of my c172, I have a COG range of forward 35.0 aft of datum at 1950lbs or less, with straight line variation to 40.0 inches aft of datum at 2450lbs
The aft range is 47.3 of datum at all weights.
What does this mean.
The datum is the imaginary vertical plane where the horizontal distance is measured.
The ranges above means that my COG that I calculate after doing a weight and balance should fall between that range and those numbers are the maximum and minimum of those limits?

source: own work
It means that your centre of gravity needs to be in the hatched area of the diagram. I've assumed an empty weight of 1600lb for the C172.
You have to calculate the weight of the aircraft and the position of the C.o.G. and verify it is within the correct range as depicted.

Thank you. I was just making sure.

You're welcome! The normal way of showing appreciation for an answer at this site is to upvote, and if it answers your question, you could accept the answer by clicking the checkmark below the voting buttons. Please wait at least 24 hours before accepting an answer, to give people around the globe some time to put in their answers and comments.

ok. So for the chart above the forward limit at 1600lbs is 35.0 inches and aft is 47.3 whilst at 2450lbs the forward limit is 40.0?

@youngpilot, yes. That's the right interpretation.


text:
How to become a master at multitasking
I am a student pilot with 60 hours. The first 50 hours I received 5 years ago and the last 10 is what I have received within the past month.
I need some advice:
Throughout training My instructor points out I do well, however when flying I forget certain things and its like my mind goes blank for a second. Blank in the sense of not knowing what to do next.
My question is how can I become a better pilot with great multi-tasking skills even with radio calls I would get. I am familiar with the calls, but there are some calls tower sends out that throws me for a loop. I am feeling discouraged but I know that this is what I want to do for a living because I love it. Please help

I agree that repetition is the key, this will improve with practice. Don't worry about it too much, just remember Aviate, Navigate and Communicate. Relax and enjoy flying and this will come on its own.

Practice, prioritising & planning.

John K is correct in that repetition is the key. The trick is to repeat and rehearse until certain tasks become automated because surprise surprise, when it comes to non-automated functions, humans actually are unable to multitask. When performing multiple tasks that require focus and thought, people resort to switchtasking, which is costly:
Multitasking: switching cost

According to Meyer, Evans and Rubinstein, converging evidence suggests that the human "executive control" processes have two distinct, complementary stages. They call one stage "goal shifting" ("I want to do this now instead of that") and the other stage "rule activation" ("I'm turning off the rules for that and turning on the rules for this"). Both of these stages help people to, without awareness, switch between tasks. That's helpful. Problems arise only when switching costs conflict with environmental demands for productivity and safety.

Your current "problem" lies within the fact,that many of the tasks required by successfull operation of an aircraft are not sufficiently automated yet, so the switching cost becomes very high. Over time with practise/repetition the switching cost will become lower, and some tasks will become fully automated only requiring an impulse to set the task sequence in motion.
There are huge variations across individuals on how quickly one learns new tasks to cut down or omit the switching cost. That's totally normal.

Thank you everyone for your input. I will use this knowledge to become more proficient and being a better pilot.

A major factor in your situation is the very long pause you had during your training. You basically know what you are doing, it just takes time to make it all "easy" again

The trick is repetition repetition repetition, and drill drill drill.  You need to drill all of the tasks, data and procedures that you more or less know, but are not fully internalized, or automated mentally, until they are fully programed and automated in your brain.
Get in the habit of repeating things you have to be able to recall from memory all the time, while driving, or whatever, like an engine failure drill.  Get to where you can recite things you have to recall from memory in emergencies while someone physically distracts you somehow, say by talking over you and even poking you while you do it.
Use MS Flight Simulator and practice activities on that. Computer sims are a very powerful tool for getting the repetition required to internalize tasks.  It's when the tasks are fully internalized through repetition so that they come to you without thinking, you gain the ability to act while thinking ahead to what to do next.
When the instructor does some kind of nasty trick, your hands fly around the cockpit automatically, while you think through your next steps or options, while telling the instructor what you're thinking. Getting to that level is like acquiring a superpower.
Really, your instructor should be teaching you this as part of your training.

Regarding engine failure drill, don't forget to train the initial reaction to push the nose down and establish safe gliding speed. Even very experienced pilots often say it's quite hard to resist the urge to pull up and stretch the glide, but obviously physics won't let you get away with that.

And you could say that's the whole point about drill drill drill. It leaves your mind free to fly the plane AND think ahead to the missed approach procedure while your hand flies around doing this and that. When I was flying CRJs, it was very infrequent, 100 hrs a year, and I got a lot of mileage out of a $40 CRJ simulator for WIndows and an elaborate homemade control column/thrust lever apparatus I built that gave me the luxury of doing hundreds of V1 cuts and MAs at home. When recurrent came up, I was calm and cool doing emers, like an experienced capt.

This is called mental overload, and believe me it happens to every pilot. In fact it happens to every person who has ever tried to do multiple complex tasks concurrently.
Our brain is good at concentrating on doing one thing well, and when you try to bring in other things then the brain has to share its ability to process those tasks and often this can lead to dropping parts of one of the tasks that the brain feels is unnecessary.
The way around it is to get the brain to perform some of the tasks autonomously - that is to say without having to consciously concentrate on doing them. If you've ever gotten from A to B in a car and thought "Hold on, I don't remember getting here I was thinking about something else" that is because driving has become somewhat autonomous. You were probably not unsafe in getting there, but you didn't have to concentrate on the task of accelerating, braking, looking at junctions etc.
Flying is the same. Once you have practiced more and more, many of the acts of flying become semi-autonomous. Like the act of just staying straight and level, a task you no doubt have to concentrate on getting right at the moment will become more natural, allowing your brain to be freed up to process some of those radio calls.
Practice makes perfect, in every sense.
I've shared this little quip a few times; the act of actually flying an aeroplane is the easy bit. It's all the other stuff going on at the same time which is the hard bit. The bit that requires practice. The radio is one of those "bits". I can honestly say that I learn almost as much sitting next to another pilot while they are flying than I do in the left hand seat. Gives you much more mental capacity to listen to what is going on. See if you can find a flying buddy and share some flights - or sit in on another student's lessons in the back if that's a possibility.

In the airplane, or FTD - there’s an exercise called the Oscar pattern. It’s useful in developing that initial instrument scan that works your task switching and ability to handle workload while saturated.
At home, I study, and recommend all pilots study, while bouncing a racquet or tennis ball against a wall. To this day, 24 years into an airline career, I study my Immediate action items and emergency procedures- and even the regular checklists and flows I do every day while bouncing the ball. I’m a check pilot at a major airline, and now and then have to sit right seat. But not often. I study those flows the night before a trip bouncing and catching the ball off a wall. If I hesitate on the IAS or flow, I start over. If I drop the ball, I start over. Once that’s easy, I do it standing on one foot or with the nerf football - something that challenges the hand eye coordination more.
I brought this technique from my basketball days they called “dual task orienting” which Steph Curry has made famous. You ever see him dribbling a basketball and a tennis ball with a blindfold that has strobes? - Why would a professional basketball player need to be able to dribble a tennis ball? It’s a worthy google search- what you dont see is he’s also getting drilled on his plays and sets that he has to know while doing that. Mental while loading up his hand eye coordination.
Anyone can know their procedures sitting at a desk. But can you recite something mentally challenging while doing something physical that requires your hand eye coordination? There’s no better exercise for this than flying itself- but if you want that to be a funner more proficient experience, this is a good exercise to do at home.
I can’t say I know the science, but I’ve been told it’s nervous system training. Connecting synapses that lead to proficiency. I don’t know, but I know it has worked for me and many of my peers and students. Every instrument student knows the feeling of developing a scan. At first you’re all over the place, but with practice your scan gets quicker, your eyes move where they need smoother and it all starts to slow down.
It’s the same process as a student pilot getting that initial control where you widen your field of perception.
Good luck and hope that helps.


text:
Did I calculate this fuel consumption correctly?
My PPL oral exam study guide contains this question:

If gallons-per-hour is 9.3 and time is 1 hour, 27 minutes, how many gallons will be consumed?

The book says 3.5 gallons, but im getting 13.5 gallons when I do the calculation using my E6B.

Voting to close as this is an inappropriate question for SE.Aviation. It's a fair question to ask of the experts, but IMHO this isn't the kind of question which passes the litmus test of "will it be useful for people 5 years from now, and so should we forever memorialize it?" Maybe @OP should bring it to the chat, instead of asking it in our Q&A.

If there is a PPL study guide with an incorrect answer, it is possible that someone else with the same book will notice the discrepancy as well and Google it or search here, so I believe it this question is appropriate for the site.

@Someone I see your point, although I personally disagree that we should enshrine permanently every typo in every book. However, I think we can both agree that none of that information is in the question, and conclude this question doesn't meet either of our standards.

$$ \text{1:27} = \text{1 hour} + \text{27 minutes} \cdot \frac{\text{1 hour}}{\text{60 minutes}} = \text{1.45 hours} $$
$$ \text{1.45 hours} \cdot \frac{\text{9.3 gallons}}{\text{1 hour}} = \text{13.485 gallons}$$
Your answer is correct; the book is wrong.

1:27 is 1.45hr, times 9.3 is 13.49, so the computer is right. You should be able to guess it in your head to 13 +/- 1 (one and a half times nine).  3.5 is obviously a typo with the one missing.


text:
Is there a somewhat realistic FOSS flight simulator for Linux?
Are there any free and open source flight simulators for Linux that are fairly realistic (i.e. if I play one for a while, I will have some idea of how flying a real plane works)? The only "flight simulator" (if you can call it that) I've tried is the one in Wii Sports Resort; even with my very minimal understanding of flying, I know it is not done by tilting a Wii remote, and you should not fly inside volcanoes.

This question might get closed as off topic as it is asking for recommendations, but I personally have found FlightGear to be decent.

Why is "free and open source" important? Real flying costs real money, too, but still: Simulators are much cheaper, specifically crashes. ;-)

@U.Windl I prefer to use open source software when possible, and "real flying costs real money" is why I don't plan to fly a real plane in the foreseeable future.

From Wikipedia:

FlightGear Flight Simulator (often shortened to FlightGear or FGFS) is a free, open source multi-platform flight simulator developed by the FlightGear project since 1997.

David Murr started the project on April 8, 1996. The project had its first release in 1997 and continued in development. It has specific builds for a variety of operating systems including Microsoft Windows, macOS, Linux, IRIX, and Solaris.
FlightGear is an atmospheric and orbital flight simulator used in aerospace research and industry. Its flight dynamics engine (JSBSim) is used in a 2015 NASA benchmark to judge new simulation code to the standards of the space industry.

The level of realism depends on the aircraft used. There is anything from arcade style to realistic A320 or the shuttle.

To be fair, if NASA is using it, it's gotta be pretty good.

@FreeMan. I think there are a couple of steps missing in your reasoning.

I just installed FlightGear, and I would definitely have no idea how to fly a plane.

@FreeMan, there are two parts to a simulator: the engine and the models. The JSBSim engine (the part of FlightGear that handles flight dynamics) is good, but it has to be provided all the aerodynamic coefficients. The models provide those, and there is a lot of them. Some are quite accurate, some are just guesses (there is even a coefficient-guessing tool based on Roskam's books). And even for the good ones the coefficients tend to only be provided in the normal flight envelope, so stall and spin behavior is … way off (not simulated at all, mostly).

@FreeMan … there is also the Yasim engine, which tries to guess the coefficients itself from the shape and weight distribution, and does it even outside the normal flight envelope, but it does not implement any compressibility effects, so it's only decent for slow aircraft.

I know it is not done by tilting a Wii remote

Actually, with FlightGear, you should be use Wii remote with a headtracking addon, to look around and/or point & manipulate cockpit controls. Linuxtrack supports it. Might need a bit of IR reflective tape or IR led.
Looking around and using it on the default C172P should look something a bit like this youtube video

that are fairly realistic

Like Jim NASA said FlightGear is as realistic as it can get [for an available space industry standard flight dynamics engine] - with better developed aircraft FDMs. Use the launcher to filter by FDM and Systems. Look at JSBSim planes especially, at the beginning.
Look at the Fightgear wiki, and this youtube tutorial playlist to get off the ground
Edit: looking at it, new user section of wiki has updated aircraft recommendations